Running both Magnum 350 & Fluval 404 on a 180 gallons planted tank

[Toffee]

Can Any one help me with this:

I have a Magnum 350 & Fluval 404, I would like to use them on a newly
acquired 180 gallons (6'x2'x2') tank with built in overflow I am thinking
of doing the following, which one is more feasible?

Option 1.
Overflow > buffer container (5 gallons?)
both 350 & 404 suck from buffer and pump back to tank.

Option 2
Overflow > buffer container
350 sucks from buffer and pump to buffer container #2
404 sucks from buffer #2 and pump back to tank
(using 350 as a mechanical & 404 as bio)

Option 3
Overflow direct connect (pipe>adaptor>hose) to 350
350 direct connect (hose>adaptor>hose) to 404
404 to tank
(will this setup hurt the motors of 350 & 404?)

This tank will be fairly haeavily planted.

Any advise is appreciated.

Thanks